Coulomb Excitation Studies of Radioactive 20,21 Na

Coulomb Excitation Studies of Radioactive 20,21Na

Douglas Clinefor the TIGRESS Collaboration

CAP Congress; Saskatoon, June 18, 2007

Bambino

TRIUMF/ISAC2

SCIENTIFIC GOALS:

Recommendations of the 2007 NSAC Long-Range Plan

• What is the nature of the nuclear force binding stable and exotic nuclei?

• What is the origin of simple patterns in complex nuclei?

• What is the nature of neutron stars and dense nuclear matter?

• What is the origin of the elements in the cosmos?

• What are the nuclear reactions that drive stars and stellar explosions?

CAP Congress Saskatoon, 18 June 2007 Douglas Cline for TIGRESS Collaboration

Reaffirmed construction of a next-generation radioactive beam facility which is central to nuclear science. It will allow study of nuclei far from stability and address the following fundamental questions:

How does structure evolve at extremely large neutron number?


neutrons

protons

rp p

roce

ss

rp p

roce

ss

Crust

proces

ses

Crust

proces

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n-Star

KS 1731-260

s-pro

cess

s-pro

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r processr processr processr process

stel

lar bu

rnin

g

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gp pro

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p proces

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Supernova

E0102-72.3

Time (s)

X-ray burst

331

330

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328

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Fre

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10 15 20

4U1728-34

Nova

T Pyxidis

Impact of Nuclear Structure on nucleosynthesis

Thanks to Witek Nazarewicz, U. Tennessee


THE SCIENCE

• Probe collective and single-particle properties of exotic nuclei

• Eλ and M1 matrix elements are sensitive probes of both collective and single-particle degrees of freedom in exotic nuclei.

• Fast recoiling exotic nuclei, produced by projectile fragmentation, have been used in pioneering measurements of “B(E2:2+→0+) “ values in nuclei far from stability via unsafe Coulomb excitation.

• Current goal is to Coulomb excite exotic beams at safe bombarding energies where the reaction mechanism is fully known allowing accurate determination of Eλ and M1 transition strengths plus static E2 and M1 matrix elements of excited states.


COULOMB EXCITATION

Coulomb excitation is the preeminent probe of collective shape degrees of freedom:

• Selectively populates collective states in the yrast domain

• Reaction mechanism fully understood if below the Coulomb barrier

• The cross sections are directly and unambiguously related to the Eλ matrix elements

• The Eλ matrix elements are the most direct measure of λ-pole collectivity


Major advances in the Coulomb Excitation Technique

1. Availability of prolific source of ~ 4.5 MeV/A variable energy exotic heavy-ion beams; TRIUMF/ISAC2

2. Development of powerful γ-ray detector and heavy-ion systems for high-resolution γ-ray spectroscopy: TIGRESS, Bambino

3. Development of the Coulomb excitation least-squares search code GOSIA*

*[Czosnyka, Cline, Wu, 1980]


Coulomb Excitation Technique

Experimental Method:

• Use thin targets so that excited nuclei recoil in vacuum

• Measure scattering angles and velocities of recoiling ions over a wide range of scattering angles

• Detect deexcitation γ-rays in coincidence with the scattered ions.

• Normalize projectile excitation to target excitation using an accurately known B(E2)

Deduce:

• Masses and velocity vectors of recoiling ions, reaction Q-value

• Correct for Doppler shift of de-excitation γ-rays on an event-by-event basis

• Identify which γ-rays are emitted by each recoiling ion

• Determine Coulomb excitation cross sections to excited states as function of impact parameter.

• Use GOSIA2 to extract individual electromagnetic matrix elements from measured yields for both target and projectile excitation.


Coulomb excitation observables

• Determine B(E2), B(E3), and B(M1) values

• Determine sign and magnitude of static E2 moments of excited states

• Determine signs and magnitudes of observable products of Eλ matrix elements

• May extract M1 moments of excited states from the measured attenuation of the γ-ray angular correlations for ions recoiling in vacuum

ISAC Production Accelerator

TRIUMF500 MeV

Cyclotron100 A

high-energy proton beam

Thick/Hot Target

Ion Source

Isotope Separator

IonBeam60 keV

DTL1

RFQ

Accelerated Beam0.15 – 1.7 MeV/A

8 Spectrometer

TIGRESS @ ISAC-I

DTL2

High SCRF

Med SCRF

LowSCRF

SC

LINAC

0.15 – 5.0 MeV/A

TIGRESS @ ISAC-II

• TRIUMF

• ISAC

• Gamma

• Ray

• Escape

• Suppressed

• Spectrometer

A Next-Generation Gamma-Ray Spectrometer for ISAC-II


TIGRESS

Optimal SuppressionMaximum EfficiencyrGe = 11.0 cm = 17% @ 1 MeV

rGe = 14.5 cmrBGO = 11.0cm

Twelve 32-fold segmented Clover DetectorsFour 40% HPGe crystals per clover.


Bambino Si CD Heavy-ion detector(LLNL; Rochester)

• Forward and backward annular Si CD heavy-ion detectors

• Angular coverage:

20o < θ < 50o, 130o < θ < 160o

00 < φ < 315o

• Angular resolution;

Δθ = 1.22o, Δφ = 22.5o


First TIGRESS Experiment: Coulomb excitation of 20,21Na, 21Ne

Technical Goal:• Commission TIGRESS, Bambino, Digital signal-processing data acquisition system

• Evaluate optimal geometry, technique, and backgrounds.

Scientific goal:• Study 5p-0h T = ½ configurations to constrain calculations of the 5p-2h 3/2+

resonance at 4.033 MeV in 19Ne. This resonance could provide a gateway from the hot-CNO cycle to the rp-process in nova, x-ray bursts.

NB:

• Accurate lifetime measurements of the first excited 5/2+ states are available

• Neither 21Na and 21Ne have been Coulomb excited previously.

• Inaccurate E2/M1 mixing ratios poorly determine the B(E2) transition strengths.

For 21Na the B(E2:5/2→3/2)* = 48 ± 41 e2fm4

* R.B. Firestone, Nuclear Data Sheets 103 (2004)269 plus NNDC 10/10/2006 erratum


First TIGRESS Experiment: Coulomb excitation of 20,21Na, 21Ne

• Performed August 2006 using ISAC1, ran one week each for 21Na and 20Na

• 1.700 MeV/A beams, incident upon a 520μg/cm2 NatTi self-supporting target

• 108 ions/second of 21Na was available. Electronics limited beam to 5 x 106 ions/second

• 2 x 106 ions/second of 20Na delivered on target

• Used two TIGRESS modules at θ = ±900 plus Bambino at 20o < θHI <50o

Bambino Θ = 20-50o

Pb shielding

1x10cm collimato

r

plastic scintillat

or

First TIGRESS Experiment: Coulomb Excitation of 20-

21Na,21Ne, Aug 2006

160 Channels of custom 14 bit, 100 MHz digitizers

2 HPGe clovers + BGO suppressorsSilicon CD-S2, 4 TIG-10 cards2 collector cards + master TIG-C

Digital Data Acquisition Fully Implemented:

21Ne, 21Na Heavy-ion gated γ-ray Spectra


• Clean γ-ray spectra with negligible influence of 511 keV due to intense beam β+ activity

• For Ti Doppler correction shows both 46Ti and 48Ti 2+ decay transitions

Analysis of Yields with GOSIA

• γ ray yields were measured in coincidence with θ and φ gates on the recoiling ions. • Matrix elements were fit to the measured yields using the GOSIA search code assuming

the following level scheme.

R.B. Firestone, Nuclear Data Sheets 103 (2004) 269.


Comparison of data with GOSIA for 48Ti Analyzed assuming B(E2;2+ → 0+) = 144 (8) e2fm4

21Ne Beam

21Na Beam

← vs →

← vs →

GOSIAGOSIA

984 keV

0+

2+


48Ti

21Ne Coulomb Excitation

351 keV

GOSIA

B(E2)↓for 5/2+ → 3/2+g.s. (e2fm4)Present Measurement 80 ± 6Previously Accepted 83 ±10


21Na Coulomb Excitation

332 keVGOSIA

B(E2)↓for 5/2+ → 3/2+g.s. (e2fm4)Present Measurement 124 ± 9Previous 48 ±41


Comparison of Results with Prior Work


21Ne Present work Prior work [1]

B(E2; 5/2+ →3/2+) 80 ± 6 e2fm4 83 ± 10 e2fm4

δ(E2/M1) (5/2+ →3/2+) - 0.073 ± 0.003 - 0.074 ± 0.004

21Na Present work Prior work [1]

B(E2; 5/2+ →3/2+) 124 ± 9 e2fm4 48 ± 41 e2fm4

δ(E2/M1) (5/2+ →3/2+) + 0.084 ± 0.003 + 0.05 ± 0.02

[1] R.B. Firestone, Nuclear Data Sheets 103 (2004) 269 with NNDC 10/10/2006 erratum

Interpretation of E2 Collectivity in 20 < A < 24 nuclei

Weisskopf E2 single-particle estimate:

Observations:

• Strong E2 enhancement ranging from 9.8 to 36

• A major fraction of nuclear charge involved in collective motion

• Can these data be correlated assuming quadrupole collective deformation ?


B(E2) in Weisskopf units 21Ne 21Na

B(E2:5/2+→3/2+) 23.2 ± 2.0 36 ± 3

B(E2:7/2+→3/2+) 9.8 ± 2.2 21.4 ± 6.3

B(E2:7/2+→5/2+) 11 ± 4 18 ± 8

B(E2) in Weisskopf units 20Ne 22Ne 24MgB(E2:2+→0+) 20.3 ± 1.0 12.5 ± 0.5 21.2 ± 0.5

Macroscopic quadrupole rotor model interpretation: E2

Observations:

• Data correlated well by the simple macroscopic prolate quadrupole rotor model.

• For each nucleus the β2 values agree within the errors

• The β2 values depend smoothly with a maximum for T = 0


Effective β221Ne 21Na

B(E2;5/2+→3/2+) 0.62 ± 0.04 0.66 ± 0.03

B(E2;7/2+→3/2+) 0.59 ± 0.07 0.79 ± 0.11

B(E2;7/2+→5/2+) 0.51 ± 0.09 0.55 ± 0.14

Q3/2+ +0.62 ± 0.05 +0.27 ± 0.22

Effective β220Ne 22Ne 24Mg

B(E2;2+→0+) 0.72 ± 0.02 0.56 ± 0.01 0.61 ± 0.07

Q2+ +1.00 ± 0.13 +0.69 ± 0.12 +0.53 ± 0.02

K = 3/2+

K = 0+

Macroscopic quadrupole rotor model interpretation: M1

Observation:

• Collective model correlates the M1 data moderately well.


Observable Experiment Model

21NegK= -1.196

gR= +0.691

-0.874 (9) Fit

-0.661797 (5) Fit

+0.49 (4) +0.51

21NagK= +2.710

gR= +0.662

+0.950 (9) Fit

+2.38630 (10) Fit

+3.7 (3) +2.97

Microscopic shell model interpretation

Shell model predictions in the complete 2s-1d shell were made using OXBASH plus the USD residual interaction. Effective charges of en = 0.5e and ep = 1.5e were used to account for core polarization. [C. Barbieri, Private communication]

Observations:

• Observe BE2 in 21Na is stronger than in 21Ne as is predicted.

• Shell model B(E2) values require a slightly larger polarization charge

• Shell model B(M1) values require to be slightly quenched.


21Ne 21NaExperiment Shell model Experiment Shell model

80 ± 6 72.8 124 ± 9 92.1

0.1274 ± 0.0025 0.158 0.1504 ± 0.0018 0.208


Science implications for 21Ne and 21Na

• The measured B(E2;5/2+→3/2+) values in 21Na and 21Ne are strongly enhanced.

• The implied very large prolate quadrupole deformation leads to the E2 properties that are correlated well by the naïve quadrupole collective rotor model.

• The large effective deformations derived assuming the naïve quadrupole rotor model are consistent with values in nearby even-even mass nuclei 20, 22Ne and 24Mg

• The M1 properties also can be understood by the collective model.

• Microscopic shell model calculations in the 2s-1d valence space are able to predict the strong quadrupole collectivity if a large polarization charge is assumed.

Coulomb Excitation at the Proton-Dripline: 20Na

600 3+

799 4+799199

600

Involved in the CNO breakout via: 15O(a,γ)19Ne(p,γ)20Na

Spectroscopy performed using GS+FMA; D. Seweryniak et al., PLB 590, 170 (2004)

No transition matrix elements are known

Gated p-γ TIGRESS spectrum


CONCLUSIONS

• TIGRESS commissioning experiments at ISAC-1 were a tremendous success

• Intense radioactive beams of 20, 21Na produced by TRIUMF/ISAC-1

• TIGRESS and Bambino, plus the digital signal-processing system performed well.

• The technique provided high-quality and significant scientific results. This bodes well for the planned exotic beam Coulomb excitation program at TIGRESS

Acknowledgements

M.A. Schumaker1, A. Andreyev2, R.A.E. Austin3, G.C. Ball2, D. Bandyopadhyay1, C. Barbieri2, J.A. Becker4, A.J. Boston5, H.C. Boston5, R. Churchman2, F. Cifarelli2, D. Cline6, R.J. Cooper5, D.S. Cross7, D. Dashdorj8, G.A. Demand1, M.R. Dimmock5, T.E. Drake9, P. Finlay1, A.T. Gallant3, P.E. Garrett1,2, K.L. Green1, A.N. Grint5, G.F. Grinyer1, G. Hackman2, L.J. Harkness2,5, A.B. Hayes6, R.

Kanungo2, K.G. Leach1, G. Lee2,9, R. Maharaj2, J-P. Martin10, F. Moisan11, A.C. Morton2, S. Mythili2,12, L. Nelson5, O. Newman2,13, P.J. Nolan5, E. Padilla-Rodal2, C.J. Pearson2, A.A. Phillips1, M. Porter-

Peden14, J.J. Ressler7, R. Roy11, C. Ruiz2, F. Sarazin14, D.P. Scraggs5, C.E. Svensson1, J.C. Waddington15, J.M. Wan7, A. Whitbeck6, S.J. Williams2, J. Wong1, C.Y. Wu4

1Department of Physics, University of Guelph, Guelph, Ontario, N1G 2W1, Canada2TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, V6T 2A3, Canada

3Department of Astronomy and Physics, St. Mary's University, Halifax, NS, B3H 3C3, Canada4Lawrence Livermore National Laboratory, Livermore, California, 94551, U.S.A.

5Department of Physics, University of Liverpool, Liverpool, L69 7ZE, U.K.6Department of Physics and Astronomy, University of Rochester, Rochester, NY, 14627, U.S.A.

7Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, V5A 1S6, Canada8Department of Physics, North Carolina State University, Raleigh, North Carolina, 27695, U.S.A.

9Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, Canada10Département de Physique, Université de Laval, Québec, Québec, G1K 7P4, Canada

11Département de Physique, Université de Montréal, Montréal, Québec, H3C 3J7, Canada12Department of Physics and Astronomy, University of British Columbia, BC, V6T 1Z1, Canada

13Department of Physics, University of Surrey, Guildford, Surrey, GU2 7XH, U.K.14Physics Department, Colorado School of Mines, Golden, Colorado, 80401, U.S.A.

15Department of Physics, McMaster University, Hamilton, Ontario, L8S 4L8, Canada

Funding provided by:Natural Sciences and Engineering Research Council of Canada

U.S. Department of Energy through University of California, Lawrence Livermore National LaboratoryU.S. Department of Energy

U.S. National Science FoundationU.K. Engineering and Physical Sciences Research Council

TRIUMF funded by the National Research Council of Canada




TIGRESS FUTURE PLANSJuly-August 2007:

- Coulomb excitation of 28,29Na beams from ISAC-II

- 6 TIGRESS modules plus two Bambino Si CD detectors

2008 →

ISAC-II: - Charge-state booster will allow A < 150 beams

- Actinide target will produce higher isotopic yields

TIGRESS: - 12 detector modules completed in 2009

Auxiliary detectors:

- SuperCHICO (LLNL, Rochester)

- DESCANT, deuterated scintillator neutron detector array (Guelph)

- EMMA, a recoil mass spectrometer (TRIUMF)

- Bragg detector (York)

- DSSD Barrel (York, Colorado)

- CsI(Tl) (St Mary’s)


Semiclassical least-squares Coulomb excitation search code GOSIA

T. Czosnyka, D. Cline, C.Y. Wu University of Rochester

Developed in 1980 at Rochester. Codes and manual for GOSIA can be obtained from the website:

http://www.pas.rochester.edu/~cline/Research/index.html

Look under links > Techniques > GOSIA to obtain:

GOSIA MANUAL: Describes the June 2007 version of the complete set of GOSIA codes

GOSIA UPDATES: Lists the most recent updates to the GOSIA Manual and associated codes.

GOSIA CODES:• GOSIA is the Fortran source code for the June 2006 version of the basic code.

• GOSIA2 is the Fortran source code for the June 2006 version of a special version of GOSIA designed for use when analyzing simultaneous Coulomb excitation with a common normalization. This is useful for determining transition strengths in radioactive beams by normalization to a known transition strength in the target.

• PAWEL is the Fortran source code for the June 2006 version of a special offspring of GOSIA designed to handle cases where a fraction of the nuclei have an excited isomeric state as the initial state.

• ANNL is a special version of GOSIA, developed by Rich Ibbotson, that uses simulated annealing techniques to locate minima.

• SIGMA is the Fortran source code for deducing the quadrupole invariants from the E2 matrix elements determined by GOSIA.

Documents

Coulomb Excitation Studies of Radioactive 20,21 Na